1. Field of the Invention
The present invention relates to a control unit. More specifically, the present invention relates to a control unit having a collision judgment function for judging that a main shaft of a machine tool has collided with other objects.
2. Description of the Related Art
A main shaft of a machine tool or an arm of a robot may unexpectedly collide with other objects due to a program error or an error in operation made by an operator in some cases. In the case of a collision, the main shaft or the robot arm, and a motor for driving the main shaft or the robot arm may be damaged. In this case, machining and operation accuracy are affected. Therefore, when a collision occurs, it is desirable that the machine tool or the robot be stopped and checked.
According to Japanese Unexamined Patent Publication No. 2-179479, the following countermeasure is disclosed. Since the main shaft and the motor to drive the main shaft are abnormally vibrated when the main shaft of the machine tool etc., is damaged, an abnormal vibration is detected by a position detector provided on the main shaft. Further, according to Japanese Unexamined Patent Publication No. 2006-138756, the following countermeasure is disclosed. In the case where a maximum value of an output signal sent from a vibration sensor attached to a main shaft etc., of a machine tool exceeds a threshold value, it is judged that a collision of the main shaft with other objects has occurred.
In Japanese Unexamined Patent Publication No. 2-179479 and Japanese Unexamined Patent Publication No. 2006-138756, it is possible to detect a collision without being linked with a control unit for a machine tool. In other words, in Japanese Unexamined Patent Publication No. 2-179479 and Japanese Unexamined Patent Publication No. 2006-138756, an output signal of a vibration sensor at the time of the occurrence of a collision is not related to the operation information of the machine tool, for example, the operation program.
However, in the case where the machine tool is automatically operated, specific circumstances at the time of collision are unknown. Therefore, it is difficult to determine a cause of the collision. Even when the machine tool is manually operated by an operator, unless the operator reports that the collision has occurred, it is also difficult to determine the cause of the collision, since the specific circumstances at the time of collision are unknown.
The present invention has been accomplished in the light of the above circumstances. An object of the present invention is to provide a control unit capable of knowing a specific circumstance of collision occurred in a machine tool and quickly determining the cause of the collision.